Odor free, air dry, aqueous emulsion paints

ABSTRACT

An aqueous ambient dry paint coating based on vinyl acetate matrix polymer containing an oligomer selected from a polyurethane or a polyester having a Tg below -20° C. and a number average molecular weight between 200 and 20,000, where the coating is free of organic coalescing solvents. The matrix polymer is produced by mixing the oligomer with the vinyl acetate monomer and other ethylenic monomers, if any, to form an organic mixture of monomer and oligomer, providing an aqueous micro dispersion of the organic mixture phase droplet size less than 5 microns, and copolymerizing the monomer to produce a vinyl acetate polymer containing oligomer, where the polymeric system is free of coalescing organic solvent.

This invention pertains to air dry emulsion paints based on emulsionpolymeric binders and more particularly to odor-free, consumer latexpaints free of polluting offensive odoriferous coalescing solvents.

BACKGROUND OF THE INVENTION

Paint coatings are surface protective coatings applied to substrates,dried to form continuous films for decorative purposes as well as toprotect the substrate. Consumer paint coatings are air-drying aqueouscoatings applied primarily to architectural interior or exteriorsurfaces, where the coatings are sufficiently fluid to flow out, form acontinuous paint film, and dry at ambient temperatures to protect thesubstrate surface. A paint coating ordinarily comprises an organicpolymeric binder, pigments, and various paint additives. In dried paintfilms, the polymeric binder functions as a binder for the pigments andprovides adhesion of the dried paint film to the substrate. The pigmentsmay be organic or inorganic and functionally contribute to opacity andcolor in addition to durability and hardness, although some paintcoatings contain little or no opacifying pigments and are described asclear coatings. The manufacture of paint coatings involves thepreparation of a polymeric binder, mixing of component materials,grinding of pigments in a dispersant medium, and thinning to commercialstandards.

Latex paints for the consumer market ordinarily are based on polymericbinders prepared by emulsion polymerization of ethylenic monomers. Atypical consumer latex paint binder contains a vinyl acetate copolymerconsisting of polymerized vinyl acetate (80%) and butyl acrylate (20%).The hardness of the latex polymer must be balanced to permit drying andfilm formation at low application temperatures, which requires softpolymer units, while at the same time the polymer must be hard enough inthe final film to provide resistance properties which requires hardpolymer units. This is conventionally accomplished by designing a latexpolymer with a moderately elevated Tg (glass transition temperature) butthen lowering the Tg temporarily with a volatile coalescing solvent.Coalescing solvents function to externally and temporarily plasticizethe latex polymer for time sufficient to develop film formation, butthen diffuse out of the coalesced film after film formation, whichpermits film formation and subsequent development of the desired filmhardness by the volatilization of the coalescent. Internalplasticization is based on coreaction of soft monomers with hardmonomers to form a polymeric copolymer binder, such as 80/20 vinylacetate/butyl acrylate, to obtain the desired film formingcharacteristics. If a lower Tg copolymer is used without a coalescingsolvent, higher levels of soft comonomer are required leading to lowerTg polymer, and, hence, the final dried film would be undesirably soft,excessively tacky, readily stain, and readily pick up dirt.

A significant source of residual odor in latex consumer paints isdirectly due to the coalescing solvent. Coalescing solvents aretypically linear (or slightly branched) glycol ethers and esters of 7 to12 carbon atoms in length, which have boiling points typically above200° C., and solubility parameters appropriate for the latex ofinterest. One typical coalescing solvent ordinarily contained incommercial latex paints is 2,2,4-trimethylpentanediol monoisobutyrare(Texanol® Eastman Chemical Co.). The odor associated with the gradualvolatilization of this solvent is considered objectionable by consumers.Quite often the odor lingers for days or weeks after the paint isapplied and dried. All useful coalescing solvents are volatile and havesimilar objectionable characteristics. An additional deficiency inconventional exterior latex paints is the decline in crack resistance ofthe dried paint film approximately proportional to the evaporation ofthe coalescing solvent. While better coalescing solvents have aretention time of about one year in dried paint films, cracking startsto progressively appear after one year in dried paint films. Hence, theelimination of coalescing solvents and attendant objectionable odors,along with air pollution caused by volatile organic compounds (VOC), andfilm cracking deficiencies represent both a technical and marketingadvance in the state of the art of consumer latex paints.

In polymer technologies unrelated to air-dry vinyl acetate latex paints,preformed polymers have been dispersed into monomers and emulsified inwater, whereupon the monomers are then polymerized, such as disclosed inU.S. Pat. No. 4,373,054 pertaining to cathodic electrocoating, or inU.S. Pat. No. 4,313,073 pertaining to alkyd prepolymers; U.S. Pat. No.4,588,757 pertaining to laminating adhesives, or in U.S. Pat. Nos.3,953,386 and 4,011,388 pertaining to aqueous emulsion blends containingcellulosic ester/acrylic polymers.

It now has been found that certain non-volatile softening oligomericmodifiers compatible with a polyvinyl acetate matrix polymeric binder ina consumer latex paint can be retained in the dried paint filmpermanently. Softening oligomers of this invention can be incorporatedinto the paint where the oligomer will be retained permanently in thefinal paint film. Hence, the paint will not generate an odor whiledrying nor emit a residual odor from the dried paint film or otherwiseemit VOC's. The softening oligomeric modifiers of this inventionexternally modify the polyvinyl acetate and are not coreacted with thepolyvinyl acetate polymeric binder. The softening oligomeric modifiersappear to function by a chain-spacing mechanism to soften the polyvinylacetate polymers whereby the oligomeric modifiers provide lowtemperature film formation and tack-free films less prone to soiling ata given hardness and/or flexibility than ordinarily possible. A furtheradvantage of this invention enable the use of essentially all hardpolymer units of polyvinyl acetate without the need for internalplasticization (coreaction) with soft butyl acrylate polymeric units.

The present invention is based on a softening oligomeric modifiershaving a low and narrow molecular weight range where the oligomer willnot subsequently diffuse out of the matrix polyvinyl acetate polymerwhen properly dispersed into the polymeric binder phase. Preferredoligomers are non-volatile oligomers having a molecular weight betweenabout 300 and 10,000. Lower molecular weight compounds tend to bevolatile and cause excessive plasticizer migration while highermolecular weight polymers lose low temperature film-forming andsoftening effects, although molecular weights above 10,000 and in someinstances up to 20,000 can be used with softer matrix polymers.According to the process of this invention, a compatible organicsolution of oligomeric modifier in ethylenic monomer is subjected tohigh energy shear to prepare a sub-micron size organic phase dispersedinto water. Subsequent polymerization of the micronized monomer dropletsproduces a softened modified latex very different from conventionalemulsion or suspension polymerization polymers. The micro suspensionpolymerization is generally necessary with the oligomeric modifiers toaccomplish the required sub-micron aqueous emulsification of the monomercontaining the dissolved oligomeric modifier, since the oligomer willnot readily diffuse during polymerization from particle to particleacross the aqueous phase.

The principal advantage of this invention is the elimination of the odorand VOC associated with volatile coalescent solvents which areintentionally volatile and intended to migrate out of the dried paintfilm. An additional advantage pertains to dried paint films exhibitingsuperior toughness obtained through the use of a hard polyvinyl acetatematrix polymer balanced with the oligomeric modifier to accommodatesoftening through the external addition of softening modifier whileretaining the desired dried film hardness. A further advantage pertainsto lower net cost for both interior and exterior paints since high costsoft monomers can be avoided, volatile coalescing agents can beeliminated and binder volume can be increased by using a permanentnon-volatile softening oligomer instead of a volatile coalescent. Theresulting dried paint films exhibit a superior balance of hardness andflexibility while maintaining long term flexibility. These and otheradvantages of this invention will become more apparent by referring tothe detailed description and illustrative examples.

SUMMARY OF THE INVENTION

Briefly, the air-dry, aqueous emulsion paint of this invention containsan oligomeric modified binder of polymerized ethylenic monomerspreferably comprising a polyvinyl acetate polymeric binder externallymodified with a non-reactive, low molecular weight, compatible oligomerselected from a polyester-urethane copolymer, a polyether-urethanecopolymer, a polyurethane-urea copolymer, a polyester-amide, or apolyester, where above 1% and desirably between 3% and 50% by weight ofthe binder comprises softening oligomer added to the polyvinyl acetatepolymeric binder. In accordance with the process of this invention, thelow molecular weight softening oligomer has a preferred number averagemolecular weight between 300 and 10,000 and is effectively dissolved invinyl acetate monomer to form a compatible organic mixture beforeforming the polyvinyl acetate matrix polymer. The organic mixture isdispersed into water by high shear, whereupon the vinyl acetate ispolymerized to produce a stabilized latex containing the low molecularweight oligomeric modifier.

DETAILED DESCRIPTION OF THE INVENTION

The air-dry emulsion paint of this invention comprises an emulsionpolymer comprising a polyvinyl acetate polymeric binder containing anon-volatile oligomeric modifier. Suitable oligomeric modifiers inaccordance with this invention comprise low molecular weight oligomersincluding urethanes consisting of polyester-urethane copolymers,polyether-urethane copolymers, polyurethane-urea copolymers; polyesterpolymer comprising polyester-amides and polyester polymers. Theforegoing softening oligomeric modifiers function as effective externalmodifiers for latex emulsion paints, and particularly forpolyvinylacetate binder latex paints.

Useful non-volatile oligomeric modifiers have a number average molecularweight range between about 200 and 20,000, preferably between 300 and10,000 and most preferably between 500 and 5,000. A preferredcharacterization of the oligomer modifier is in units of degree ofpolymerization (DP Units) which refers to the repeating monomer unitswithout regard to molecular weight although the molecular weight ismaintained relatively low as indicated. DP units defines the approximatechain length of the oligomers without regard to side units. Theoligomeric modifier of this invention should have a DP between about 2and 100, preferably between 2 and 50 and most preferably between 2 and20 DP units. Useful oligomer modifiers have low Tg's to sufficientlyimpart a plasticizing effect on the matrix polyvinyl acetate polymer.Useful Tg's of the oligomeric modifier measured by Differential ScanningCalorimetry (DSC) at 10° C/minute scan rate are less than -20° C.,preferably less than -40° C. and most preferably below -50 ° C. Thelevel of oligomer modifier needed can vary considerably in the finallatex. The level required depends on the inherent softening efficiencyof the oligomer (estimated by its Tg) and the Tg of the matrix (parent)polymer. The Fox equation is useful for estimating the level needed:

    1/Tg (mix)=(W.sub.p /T.sub.g, p)+(W.sub.m /T.sub.g, m)

where

Tg (mix)=glass transition temperature of the modified polymer (which isa mixture);

W_(p), W_(m) =weight fraction of the parent (matrix) polymer andoligomeric modifier, respectively;

T_(g), p ; T_(g), m =glass transition temperature of the parent (matrix)polymer and the oligomeric modifier, respectively.

Thus, the level of oligomeric modifier required is directly related tothe Tg of the parent polymer, and inversely related to the Tg of theoligomer. Hence, the lower oligomer Tg will more efficiently soften thepolyvinyl acetate matrix polymer provided the oligomer and matrixpolymer are compatible. Compatibility of a polymeric mixture is commonlysaid to exist when the mixture remains substantially optically clear,which indicates the two components are mutually soluble. In thisinvention, compatibility is intended to mean that the oligomericmodifier is soluble in the matrix polymer in the solid state. Completecompatibility is believed to exist when these conditions are met: in thesolid state the mixture has a Tg (DSC, DMA) intermediate between theTg's of the two components; the absence of component Tg transitions; themixture Tg is smoothly dependent on level of modifer; and the mixture Tgfollows a mixing rule such as the Fox equation. Tg's of mixtures dependon the Tg's of the two components, concentrations of the two components,and compatibility of the two components. The present invention pertainsto substantially compatible components.

In accordance with this invention, low molecular weight polyurethaneoligomers such as polyester-urethanes, polyether-urethanes, polyetherurethane-urea copolymers, and polyester polymers includingpolyester-amide copolymers can be utilized as external softeningoligomers in the polyvinyl acetate binder matrix polymers. Usefulpolyurethane copolymers typically contain urethane groups in the polymerbackbone and are produced by reacting excess equivalents of diol orpolyol with lesser equivalents of di- or polyisocyanate. Thepolyisocyanates can be di- or triisocyanates such as for example 2,4-and 2,6- toluene diisocyanate, phenylene diisocyanate; hexamethylene ortetramethylene diisocyanate, 1,5-naphthalene diisocyanate, ethylene orpropylene diisocyanate, trimethylene or triphenyl or triphenylsulfonetriisocyanate, and similar di- or triisocyanates. The polyisocyanate canbe generally selected from the group of aliphatic, cyclo-aliphatic andaromatic polyisocyanates such as for example hexamethylene1,6-diisocyanate, isophorone diisocyanate, diisocyanate, 1,4-dimethylcyclohexane, diphenylmethane diisocyanate 2,4-toluene diisocyanate,2,6-toluene diisocyanate and mixtures thereof, polymethylene polyphenylpolyisocyanate.

Polyester-urethanes can be produced from diols comprising hydroxylfunctional polyester polymer prepared by conventional esterificationpolymerization techniques from the common dicarboxylic acids anddihydroxyl functional reactants. Suitable carboxylic acids includeadipic acid, succinic acid and anhydride, azelaic acid, maleic acid andanhydride, and other aliphatic carboxylic acids. Aromatic dicarboxylicacids include isophthalic acid, phthalic acid and anhydride,terephthalic acid, trimelitic anhydride and the like. Lesser amounts ofmono-functional acids can be included, such as benzoic acid,2-ethylhexanoic acid, if desired. Suitable dihydroxy functionalmaterials include ethylene and propylene glycol, dipropylene glycol,diethylene glycol, neopentyl glycol, trimethylol propane, and lesseramounts of mono-functional alcohols such as benzyl alcohol and hexanol,if desired. Polyester prepolymers are generally prepared with excesshydroxyl functionality at molecular weights ranging from about 100 to10,000 preferably about 200 to 2,000. Polyester prepolymers can be usedalone or in combination with polyethers as hydroxyl functionalprepolymers. Suitable hydroxyl functional polyether prepolymers includepolyethylene oxide, polypropylene oxide, polybutylene oxide, andtetramethylene oxide where the polyether prepolymers have a molecularweight between about 100 and 10,000.

The polyesters and/or polyether prepolymers are then reacted withdiisocyanate to advance the prepolymers to a molecular weight of about200 to 20,000 and preferably between 300 and 10,000 to form polyester orpolyether urethane oligomers of this invention. Diisocyanates are usedpreferably at an equivalent ratio of about 1 isocyanate group to 1.1 to10 hydroxyl groups. Ratios of about 1.5 to 3 hydroxyl groups perisocyanate group are preferred. Preferred diisocyanates include toluenediisocyanate, isophorone diisocyanate, 1,6-hexane diisocyanate,diphenylmethane diisocyanate, and the like. Catalysts such asdibutyltindilaurate, tin oxide and the like can be used to increase theisocyanate reaction rate with the hydroxyl polyester or polyetherprepolymer at temperatures of about 30° to 120° C. and preferably atabout 70° to 100° C.

The polyester or polyether urethane copolymers can be further extendedwith diamine or polyamine, if desired, to produce polyurethane-ureacopolymer useful as a softening oligomer modifier in polyvinyl acetatebinder matrix polymers in accordance with this invention. In thisregard, primary diamine or polyamine can be added to an isocyanateterminated polyurethane intermediate containing unreacted pendant orterminal isocyanate groups obtained by reacting excess equivalents ofisocyanate relative to hydroxyl equivalents in the polyester orpolyether prepolymers. The primary diamines readily react with theisocyanate functional intermediate to chain extend the polyurethane to apolyurethane-urea of a higher molecular weight. Alternatively amine canbe prereacted with the diisocyanate prior to reacting with polyol.Suitable primary amines for chain extension include hexamethylenediamine, 2-methyl-pentanediamine and similar aliphatic diamines.Polyester and polyether urethane copolymers or polyurethanes extendedwith diamine to form polyurethane-ureas exhibit excellent compatibilitywith vinyl acetate monomers as well as the resulting polyvinylacetatepolymers. Polyurethane intermediate molecular weights before chainextension can be between 400 and 10,000 while after chain extension withthe diamine the final molecular weight of the polyurethane-urea can bebetween about 800 and 20,000.

In accordance with this invention, the polyurethane copolymers can besynthesized, dissolved in ethylenically unsaturated monomer such asvinyl acetate monomer, subsequently suspended in water, followed bypolymerization of the ethylenic monomers. Polyurethane oligomers can bedissolved in vinyl acetate monomers to form a fluid organic solutioncontaining above 1% and desirably between about 3% and 50% andpreferably between 10% and 25% by weight oligomer based on the weight ofthe organic monomer solution. This organic mixture of oligomer andmonomer is then suspended in water with high shear mixing to form acoarse suspension using the common latex surfactants as stabilizers,such as the sulfosuccinates, the sulfates, various ethoxylated phenols,and the like. The coarse suspension is then micronized to very fineparticle size emulsion droplets of average size of less than 5 microns,preferably less than 1 micron, and most preferably less than 0.7 micron.High mechanical shear and/or ultrasound can be used to form themicroemulsion. Typical additional ingredients include buffers, acrylicacid, sodium salt of acrylamido methyl propane sulfonic acid (NaAMPS)ordinarily added at 0.1% to 5% by weight levels based on solids.Initiators such as persulfate, peroxide, and azo initiators can be addedbefore or after suspension of the organic mixture in water. Redoxcatalysts can be added if desired. Polymerization can be accomplished bysimply raising the suspension temperature to about 70° C. to 80° C.using persulfate initiators. Initial reflux of vinyl acetate will be at67° C., but the temperature will rise with monomer polymerizationconversion. Additional vinyl acetate can be added, preferably after thepreformed suspended vinyl acetate emulsion and other monomer havepolymerized.

A further desirable non-reactive oligomer useful as a softening oligomermodifier in this invention comprises a polyester polymer. In accordancewith this invention, a low molecular weight ester or polyester can bedissolved in vinyl acetate monomer, suspended in water, and the aqueoussuspension micronized prior to polymerization of the monomers. Usefulpolyester oligomers comprise esterification reaction products of diolswith dicarboxylic acids or a functional equivalent with minor amounts ofpolyol or polyacid if desired, to produce a low acid number polyesterpolymer. Suitable esters and polyesters for blending have molecularweights between about 200 and 20,000 and include the linear and branchedesters and polyesters formed from saturated dicarboxylic acids such asadipic acid, glutaric acid, succinic acid, and other such linearaliphatic acids, acid anhydrides, and lower alkyl esters thereof;phthalic acid, isophthalic acid, trimellitic anhydride, and otheraromatic acids, acid anhydrides, and lower alkyl esters thereof;monoacids such as benzoic acid, 2-ethylhexanoic acid and other aromaticand aliphatic acids, which if desired, may be used in minor amounts toend cap and limit molecular weight. Minor amounts of unsaturateddicarboxylic acids such as fumaric or maleic acid can be included, ifdesired, to enhance grafting with polymerized vinyl acetate monomers,which promotes compatibility and permanence of the oligomer in thematrix polyvinyl acetate polymer.

Diol functional materials include diethylene glycol, neopentyl glycol,2-methyl pentane diol, ethylene glycol, butylene glycol, propyleneglycol, dipropylene glycol and the like; or mono-functional glycol ethergroups, such as butylcellosolve, butyl carbitol, and the like; as wellas hydroxy acids such as lactic acid, and lesser amounts of triols andpolyols, such as trimethylol propane and ethane, and pentaerythritol.Acids can be used in carboxyl form, anhydride form, or an ester form,such as the methyl ester form, with the above diols to form linear andbranched polyesters desirably having an Acid No. below about 20, and amolecular weight between 200 and 20,000, desirably between 300 and10,000, and preferably between about 500 and 5,000. Polyesters ofdiethylene or dipropylene glycol with adipic acid are preferred. The lowmolecular weight esters and polyesters lower the Tg of the blend and caneliminate the need for expensive comonomers such as butyl acrylate.Thus, low molecular weight esters and polyesters can be effectively usedto provide excellent, non-tacky, paint films without the inclusion ofcoalescing solvents.

Ester and polyester oligomeric modifiers described above can be easilydissolved in vinyl acetate to form a fluid organic solution above about1% and desirably between 3% and 50% by weight and preferably 10% to 25%oligomer modifer based on the weight of the organic solution. Theorganic solution of oligomer and monomer can be suspended in asurfactant treated aqueous medium by high speed prop stirring to form acoarse suspension, followed by ultrasonification or very high shear toproduce a micronized suspension and reduce the particle size of theorganic phase to about 5 microns or less, preferably less than 1 micron.Suitable surfactants are used at about 0.1 to 5% by weight (based onsolids) and include the nonionic surfactants such as various ethoxylatedphenols, block copolymers of ethylene oxide and propylene oxide, anionicsurfactants such as sulfosuccinates, sulfates, and sulfonates, and thelike (sulfosuccinates such as hexyl, octyl, and hexadecyl sulfosuccinateare preferred). Part of the vinyl acetate monomer can be polymerizedfollowed by further polymerization of the remaining monomer if desired.Common initiators are used, such as the persulfates, azos,hydroperoxides, and peroxides, at typical initiator levels andpolymerization temperatures as previously described for emulsionpolymerization.

Polyester amide oligomeric modifiers are formed by the reaction of diolsand diamines with dicarboxylic acids or esters. In a preferred process,methyl esters of adipic, glutaric, isophthalic or other commondicarboxylic acids are transesterified with diols and diamines at about150° C. to 250° C. in the presence of common esterification catalystssuch as butylstanoic acid. Typically greater amounts of diols, such asdiethylene and dipropylene glycol, neopentyl glycol and the like areused with lesser amounts of diamines, such as 1, 6-hexanediamine,2-methyl pentanediamine, or the longer chain amines (e.g.Jeffamine-Texaco). Lesser amounts of monoacids, monoesters, alcohols andamines, or polyacid, polyols, or polyamines can be added, if desired.

In accordance with this invention, the oligomer plasticizers aresolubilized in vinyl acetate monomer, then dispersed into water andmicronized into a microemulsion. The vinyl acetate monomer ispolymerized to produce a polymeric binder comprising emulsionpolymerized vinyl acetate. Selected amounts of other ethylenic monomerscan be copolymerized with the vinyl acetate monomer to produce acopolymer containing by weight less than 60% and preferably less than30% and most preferably less than 20% other ethylenic monomer.Polymerizable ethylenically unsaturated monomers containcarbon-to-carbon unsaturation and include vinyl monomers, acrylicmonomers, allylic monomers, acrylamide monomers, and mono- anddicarboxylic unsaturated acids. Vinyl esters include vinyl propionate,vinyl laurate, vinyl decanoate, vinyl butyrates, vinyl benzoates, vinylisopropyl acetates and similar vinyl esters; vinyl aliphatic hydrocarbonmonomers include vinyl chloride and vinylidene chloride as well as alphaolefins such as ethylene, propylene, isobutylene, as well as conjugateddienes such as 1,3 butadiene, methyl-2-butadiene, 1,3-piperylene,2,3-dimethyl butadiene, isoprene, cyclohexane, cyclopentadiene, anddicyclopentadiene; and vinyl alkyl ethers include methyl vinyl ether,isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether.Acrylic monomers include lower alkyl esters of acrylic or methacrylicacid having an alkyl ester portion containing between 1 to 12 carbonatoms as well as aromatic derivatives of acrylic and methacrylic acid.Useful acrylic monomers include, for example, acrylic and methacrylicacid, methyl acrylate and methacrylate, ethyl acrylate and methacrylate,butyl acrylate and methacrylate, propyl acrylate and methacrylate,2-ethyl hexyl acrylate and methacrylate, cyclohexyl acrylate andmethacrylate, decyl acrylate and methacrylate, isodecyl acrylate andmethacrylate, benzyl acrylate and methacrylate, and various reactionproducts such as butyl, phenyl, and cresyl glycidyl ethers reacted withacrylic and methacrylic acids, hydroxyl alkyl acrylates andmethacrylates such as hydroxyethyl and hydroxypropyl acrylates andmethacrylates, amino acrylates, methacrylates as well as acrylic acidssuch as acrylic and methacrylic acid, ethacrylic acid,alpha-chloroacrylic acid, alpha-cycanoacrylic acid, crotonic acid,beta-acryloxy propionic acid, and beta-styrl acrylic acid. Particularlypreferred comonomers include acrylates such as methyl, ethyl, propyl,butyl (linear and branched), 2-ethyl hexyl; methacrylates such asmethyl, ethyl, propyl, butyl (linear and branched), 2-ethyl hexyl; vinylesters such as acetate, proprionate, butyrate, pentanoate (neo 5),nonanoate (neo 9), 2-ethyl hexanoate, decanoate (neo 10); and otherethylenic monomers such as ethylene, vinyl chloride, vinylidene chlorideand butadiene.

The emulsion polymerized vinyl acetate monomer produces a matrixpolymeric binder of polymerized vinyl acetate monomer where the mostpreferred polymeric binders comprise homopolymers of vinyl acetate. On aweight basis, the polymeric binders comprise between 40% and 100%polymerized vinyl acetate with the balance being other ethylenicmonomers. Preferred polymeric binders contain at least 70% by weightpolymerized vinyl acetate and most preferred 80% to 100% vinyl acetate.The number average molecular weight of the polymeric vinyl acetatebinders should be between about 30,000 and 10,000,000 and preferablybetween 50,000 and 1,000,000 as measured by GPC (gel permeationchromatography) according to ASTM D3016-78, D3536-76, and D3593-80. TheTg or softening point of the modified polymeric binder particles shouldbe less than 20° C. as measured by differential scanning calorimetry,preferably less than 10° C., most preferably <5° C. The MFT (minimumfilm formation temperature) is an alternative measure of polymer filmformation determined on the neat latex on a temperature gradienttemperature bar, and is typically a few degrees higher than the Tg ofthe latex. MFT should be less than 20° C., preferably less than 15° C.,most preferred less than 10° C. The LTFF (low temperature filmformation) is a film forming test run on the fully formulated paint.LTFF typically is reported as the lowest temperature at which nocracking is observed, or alternatively, the amount of coalescent oroligomer needed to achieve 40° F. failure-free coatings. LTFF should beless than 50° F. (10° C.), preferably less than 40° F. (5° C.). Thedistinction with LTFF is that other paint ingredients may have either anelevating influence (fillers, pigments) or depressing (surfactants,incidental solvents in additives) effect on LTFF relative to the MFT,which is measured on the latex alone. In turn, the MFT is measured fromthe wet state, and therefore includes the plasticizing effect of water,while the Tg is measured on an anhydrous sample of latex film, whichdoes not include the water elasticizing effect. Latex paints areformulated to achieve LTFF of less than 50° F. (10° C.), preferably lessthan 40° C. (5° C.). It is also necessary for the final dried films tonot be tacky at normal use temperatures (60°-110° F.). The polymericbinder contains between about 5% and 45% by weight softening oligomerwith the balance being vinyl acetate polymer or copolymer matrixpolymer.

Historically, prior art paints achieved a balance of properties bymaking the latex slightly too hard for LTFF to achieve the tack-freecharacter, and then temporarily softening the binder polymer with acoalescing solvent to achieve the desired LTFF. This solvent thenevaporates from the film over a period of days, which allows therestoration of tack-free character. If a binder copolymer containing aninternal plasticizer is formulated to pass the LTFF test directly, thepaint will be so tacky as to be unacceptable as a paint. However, byusing non-volatile, external softening oligomers in accordance with thisinvention, the historical relationship between Tg (or MFT) and LTFF inthe final paint has changed such that both film formation and tack freecharacter are simultaneously obtained without the need for a volatilecoalescing solvent. The softening oligomer is permanent by design andwill not volatilize out of the paint film.

In accordance with the process of this invention, the preformedsoftening oligomer modifier is dissolved in the vinyl acetate monomerprior to polymerization to produce a compatible organic mixture ofoligomer and monomer. The organic mixture may further contain a freeradical initiator and is then suspended in water containing surfactantusing high shear or ultrasound to produce an emulsified mixture of lessthan 5 microns and preferably less than 1 micron emulsion phase dropletcomprising an organic phase dispersed into water. Thereafter the vinylacetate monomer and other ethylenic monomer, if any, is polymerized inan aqueous polymerization medium by adding other emulsion polymerizationingredients. Initiators can include for example, typical free radicaland redox types such as hydrogen peroxide, t-butyl hydroperoxide,di-t-butyl peroxide, benzoyl peroxide, benzoyl hydroperoxide,2,4-dichlorobenzoyl peroxide, t-butyl peracetate,azobisisobutyronitrile, ammonium persulfate, sodium persulfate,potassium persulfate, sodium perphosphate, potassium perphosphate,isopropyl peroxycarbonate, and redox initiators such as sodiumpersulfate-sodium formaldehyde sulfoxylate, cumene hydroperoxide-sodiummetabisulfite, potassium persulfate-sodium bisulfite, cumenehydroperoxide-iron (II) sulfate. Redox systems consist of oxidants andreductants, which can be mixed in any pair. Transition metals such asiron can be used as accelerators for initiators for redox couples. Thepolymerization initiators are usually added in amounts between about 0.1to 2 weight percent based on the monomer additions.

Suitable anionic surfactants include for example, salts of fatty acidssuch as sodium and potassium salts of stearic, palmetic, oleic, lauric,and tall oil acids, salts of sulfated fatty alcohols, salts ofphosphoric acid esters of polyethylated long chain alcohols and phenols.Preferred anionic surfactants include for example, alkylbenzenesulfonate salts such as sodium dodecylbenzene sulfonate and salts ofhexyl, octyl, and higher alkyl diesters of 2-sulfosuccinic acid.Suitable non-ionic surfactants include polyoxyethylene glycols reactedwith a lyophilic compound, ethylene oxide condensation products reactedwith t-octylphenol or nonylphenol and known as "Triton" surfactants,polymerized oxyethylene (IgepalCA), ethylene oxide reacted with organicacids (Emulfor), or organic acid reacted with polyoxyamylene ether ofstearic or oleic acid esters (Tweens).

The preferred process involves pre-suspension by mechanical shearfollowed by rotor-stator shear or ultrasonification to less than about 1micron. Suitable surfactants include the various sulfosuccinates such ashexyl, octyl, and hexadecyl sulfosuccinate, the various alkyl andalkyl-aromatic sulfates and sulfonates, as well as the various nonionicethylene oxide surfactants. The aqueous suspension can be generallyformed at about 10% to 60% by weight total solids. The suspension can beheated to polymerize the vinyl acetate monomer while initiator is addedif not already present in the pre-emulsion mixture. Suitable initiatorsinclude the common persulfates, peroxides, and hydroperoxides, alongwith redox initiator systems if desired. Additional vinyl acetatemonomer can be added at any time during the polymerization to increasethe particle size and raise the total solids of the system and helpcontrol the polymerization exotherm. The resulting polyvinyl acetatesuspensions containing softening oligomer can be used directly in placeof the common vinyl acetate copolymer latices in interior consumerair-dry paints.

A paint coating composition can be produced by combining the externallymodified emulsion polymer of this invention with pigments and otherpaint additives in a dispersing mill such as a Cowles disperser. Apigment dispersion can be preformed consisting of a dispersant andpigments on a disperser mill, a sand mill, a pebble mill, a roller mill,a ball mill or similar conventional grinding mill for milling themineral pigments into the dispersion medium. The premix can then becombined under low shear with the polymeric binder of this invention andother paint additives as desired. Useful mineral pigments ordinarilyinclude opacifying pigments such as titanium dioxide, zinc oxide,titanium calcium, as well as tinting pigments such as carbon black,yellow oxides, brown oxides, tan oxides, raw and burnt sienna or umber,chromium oxide green, phthalocyanine green, phthalonitrile blue,ultramarine blue, cadmium pigments, chromium pigments, and the like.Filler pigments such as clay, silica, talc, mica, wollastonite, woodflower, barium sulfate, calcium carbonate and the like can be added.

The merits of this invention are further supported by the followingillustrative examples.

EXAMPLES

Polyesters with a range of molecular weights and structures can functionas effective plasticizing and coalescing agents for poly(vinylacetate).Polymer alloys (polymer blends) of the polyesters with polyvinyl acetatepolymers form good clear films at room temperature and can be formulatedinto good air dry paints. Comonomer is not needed with vinyl acetatepolymer and coalescing aid is not required for good film formation. Thisunique approach to avoiding the use of coalescing solvents is possiblebecause the higher molecular weight polyesters are dissolved inpolyvinyl acetate monomer and then dispersed into water by high shearand/or ultrasound prior to polymerization of the polyvinyl acetate asillustrated in the following examples.

EXAMPLE 1

An adipate polyester oligomer was prepared as follows:

    ______________________________________                                                       Grams                                                          ______________________________________                                        Adipic acid      438.6                                                        Diethylene glycol                                                                              382                                                          Butylstanoic acid                                                                              0.5                                                          ______________________________________                                    

The above raw materials were heated in a 2 liter flask under a nitrogenblanket with mechanical stirring to 170° C. while using the headtemperature above a column packed with glass beads to regulate theesterification reaction. With a head temperature of 98° C., the reactiontemperature increased slowly to 220° C., where the temperature was heldfor 2 hours and then cooled.

An aqueous suspension of vinyl acetate monomer and the above adipatepolyester was prepared from the following materials.

    ______________________________________                                                           Grams                                                      ______________________________________                                        a)      deionized water  2000                                                         MM-80, Mona Chemical.sup.1                                                                     11.2                                                         (NH.sub.4) HCO.sub.3                                                                           2.5                                                          NaAMPS, Lubrizol Corp.                                                                         2.5                                                          vinyl acetate monomer                                                                          625                                                  b)      polyester from above                                                                           312                                                          MT-70, Mona Chemical.sup.2                                                                     5.6                                                  c)      (NH.sub.4).sub.2 S.sub.2 O.sub.8                                                               5.0                                                  d)      vinyl acetate monomer                                                                          625                                                          MT-70.sup.3      5.6                                                  ______________________________________                                         .sup.1 MM80 = sodium dihexyl sulfosuccinate                                   .sup.2 NaAMPS = sodium acrylamide methyl propane sulfonate                    .sup.3 MT70 sodium ditridecyl sulfosuccinate                             

Organic solution (a) was dispersed in aqueous solution (b) with a propstirrer at about 5000 rpm for 20 seconds and passed through the flowthrough cell of a Sonics Corp. model VC-600 ultrasonic device at 85%power. The resulting aqueous emulsion was heated with stirring under anitrogen blanket to 65° C. Component (c) was added and 65° C. was heldfor 1.5 hours. Monomer mixture (d) was added over 3 hours at 72° C.,held 1 hour, and then cooled.

EXAMPLE 2

In a manner similar to Example 1, a phthalate polyester oligomer wasprepared, mixed with vinyl acetate monomer, micronized into water byhigh shear, and polymerized. The phthalate polyester was as follows:

    ______________________________________                                                        Grams                                                         ______________________________________                                        phthalic anhydride                                                                              593                                                         diethylene glycol 318.3                                                       butyl cellosolve  236.4                                                       ______________________________________                                    

The raw materials were heated under nitrogen to 200° C., then slowlyraised to 220° C. over 2 hours while keeping the head temperature of thepacked distillation column at 98° C. Total distillate was 73 g. Asuspension of the above phthalate polyester was prepared as follows:

    ______________________________________                                                          Grams                                                       ______________________________________                                        a)      deionized water 800                                                           MM-80           3.0                                                           NaHCO.sub.3     2.0                                                   b)      vinyl acetate monomer                                                                         250                                                           polyester (Ex. 2 above)                                                                       80                                                    c)      K.sub.2 S.sub.2 O.sub.8                                                                       2.0                                                   d)      vinyl acetate monomer                                                                         250                                                           MT-70           3.0                                                   ______________________________________                                    

The procedure for polymerizing the ethylenic monomers was the same asdescribed in Example 1.

EXAMPLE 3

In a manner similar to Example 2, a polymer was prepared from the rawmaterial in Example 4 except that the amount of phthalate polyester wasincreased from 80 grams to 50 grams.

EXAMPLE 4

In a manner similar to Example 2, a polymer was prepared using thefollowing components using a commercial polyester believed to be apolyether-phthalate-polyester capped with benzoic acid (Hercoflex 900,Hercules Corp.).

    ______________________________________                                                          Grams                                                       ______________________________________                                        a)      deionized water 2000                                                          MM-80           15                                                            NaHCO.sub.3     2.5                                                           NaHCO.sub.3     7.5                                                           NaAMPS          2.5                                                   b)      vinyl acetate monomer                                                                         625                                                           Hercoflex 900, (Hercules                                                      Corp.)          250                                                   c)      K.sub.2 S.sub.2 O.sub.8                                                                       5.0                                                   d)      vinyl acetate monomer                                                                         625                                                           MT-70           7.5                                                   ______________________________________                                    

The procedure from Example 1 was used to produce a latex polymer.

EXAMPLE 5

In a manner similar to Example 1, a polyester triester was prepared fromthe following reactants:

    ______________________________________                                                           Grams                                                      ______________________________________                                        Ektasolve DB, Eastman Chem.                                                                        365                                                      (diethylene glycol butyl ether)                                               trimelitic anhydride 145                                                      butylstanoic acid    0.1                                                      ______________________________________                                    

The water of reaction distilled off was 29 grams.

A polymer was prepared according to the polymerization process describedin Example 3 but from the following components:

    ______________________________________                                                          Grams                                                       ______________________________________                                        a)      deionized water 800                                                           MM-80           3.0                                                           NaHCO.sub.3     2.0                                                   b)      vinyl acetate monomer                                                                         250                                                           triester from Ex. 4                                                                           50                                                            MT-70           1.0                                                   c)      K.sub.2 S.sub.2 O.sub.8                                                                       2.0                                                           vinyl acetate monomer                                                                         250                                                           MT-70           3.0                                                   ______________________________________                                    

EXAMPLE 6

Clear unpigmented films were prepared from the polymers prepared inExamples 1-5. Physical properties of latex and air dried clear paintfilms were as follows:

    ______________________________________                                                Min. Film Temp.                                                                              Min. Film Temp.                                        Suspension                                                                            Crack Point    Knife Point  Tack                                      ______________________________________                                        Ex. 3   <3             <3           None                                      Ex. 4   12             24           None                                      Ex. 5    3              9           None                                      Ex. 6   <3              6           None                                      Ex. 7    4             15           None                                      Control*                                                                              10             12           None                                      ______________________________________                                         *Control was an unmodified commercial latex typically used in consumer        airdry paints and comprising 80/20 weight ratio of vinyl acetate              polymerized with butyl acrylate.                                         

EXAMPLE 7

White semi-gloss latex paints were prepared from any one of theforegoing emulsion polymers described in Examples 1-5 from the followingingredients:

    ______________________________________                                        Pigment Grind:                                                                Group       Ingredient     Grams                                              ______________________________________                                        A           Water          151.68                                             A           Thickener      .50                                                A           Ammonia (28%)  .01                                                B           Surfactant     5.00                                               C           Defoamer       2.00                                               C           Surfactant     2.00                                               D           TiO.sub.2 pigment                                                                            145.00                                             D           Clay extender pigment                                                                        50.00                                              ______________________________________                                    

Group A ingredients were added to Cowles dispersing equipment and mixedfor 5 minutes. Group B and then C ingredients were added with continuedmixing under slow agitation. Group D ingredients were added under highspeed agitation and grind for 15 minutes or until a Hegman 5.5 wasattained. The foregoing is the grind portion of the paint.

    ______________________________________                                        Letdown      Ingredient     Grams                                             ______________________________________                                        E            Water          33.00                                             F            Water          33.00                                             F            Thickener      3.50                                              F            Ammonia Hydroxide                                                                            .01                                               G            Preservative   1.00                                              H            Defoamer       5.00                                              H            Propylene glycol                                                                             40.00                                             H            Surfactant     4.50                                              H            Rheology Modifier                                                                            9.00                                              H            Surfactant     3.00                                              I            Latex          393.00                                            I            Opacifier latex                                                                              105.00                                            ______________________________________                                    

Group E ingredients were added in separate vessel, followed by Premix Fadded to E ingredients with slow speed agitation. Group G ingredientswere added at slow speed. Premix H ingredients were then added tovessel. Premix I ingredients were mixed for 30 minutes and then added tovessel. The final composition was mixed for 1 hour. The foregoing is theletdown portion of the paint.

Latex Paint

The letdown above was added to the pigment grind above under slow speedagitation and allowed to mix for 2 hours.

EXAMPLE 8 Benzoic Acid Capped Polyester Oligomer Modifier

    ______________________________________                                        Ingredient       Grams                                                        ______________________________________                                        adipic acid      731                                                          diethylene glycol                                                                              637                                                          butylstanoic acid                                                                              0.5                                                          benzoic acid     244                                                          ______________________________________                                    

Heat the above components gradually with adequate stirring under anitrogen atmosphere to 220° C. (Water will begin to distill at about170° C., and about 3 hours will be required to move the batch from 170°C. to 220° C.). Using a packed column, maintain the head temperature at99° C. throughout this portion of the synthesis. When the headtemperature drops below 80° C., remove the column and replace with aDean-Stark trap. Fill the trap with xylene, and then add just enoughadditional xylene to give a constant reflux. Allow xylene reflux toazeotrophe water out of the batch, and reduce acid number to about 10 mgKOH/g resin. Remove xylene under a vacuum (25 inches Hg). Cool.

EXAMPLE 9 Benzoic Acid Capped Polyester Urethane Oligomer Modifier

As in Example 8, but use only 122 g benzoic acid, then cool batch to 60°C. at the end of the synthesis, and add 111 g isophorone diisocyanate.Allow the exotherm to carry the temperature (with gentle heating) to 90°C., and hold for 2 hours. Cool.

EXAMPLE 10 Polyester Urethane Oligomeric External Modifier

    ______________________________________                                        Ingredient       Grams                                                        ______________________________________                                        adipic acid      731                                                          diethylene glycol                                                                              636                                                          butylstanoic acid                                                                              0.5                                                          ______________________________________                                    

Synthesize a polyester from the above ingredients in the same manner asin Example 8, and then add 111 g isophorone diisocyanate to form apolyester urethane as in Example 9.

EXAMPLE 11 Polyester Urethane External Modifier

    ______________________________________                                        Ingredient        Grams                                                       ______________________________________                                        adipic acid       366                                                         dipropylene glycol                                                                              403                                                         butylstanoic acid 0.2                                                         ______________________________________                                    

Form a polyester from the above ingredients as in Example 8, and thenadd 56 g isophorone diisocyanate to form a urethane as in Example 9.

EXAMPLE 12 Polyester Urethane Urea Oligomeric External Modifier

    ______________________________________                                        Ingredient        Grams                                                       ______________________________________                                        adipic acid       731                                                         dipropylene glycol                                                                              805                                                         butylstanoic acid 0.5                                                         ______________________________________                                    

Synthesize a polyester from the above as in Example 8, and place 300 gof the product in a separate flask at 20° C. Add 29 g isophoronediisocyanate and 30 g Jeffamine ED-2001 polyethylene oxide diamine, 2000mol. wt. no. ave. - Texaco. The Jeffamine is predissolved in 30 g vinylacetate to enhance miscibility. Slowly warm to 40° C. to allow aminereaction with isocyanate, hold 1 hour, and then heat to 90° C. Hold 2hours, and then cool.

EXAMPLE 13 Polyester Amide External Oligomer Modifier

    ______________________________________                                        Ingredient          Grams                                                     ______________________________________                                        DBE-5 (dimethyl ester of                                                                          481                                                       glutaric acid, DuPont)                                                        dipropylene glycol  268                                                       Dytek A (2-methylpentane                                                                          58                                                        diamine)                                                                      butylstanoic acid   0.2                                                       ______________________________________                                    

Warm with good agitation under nitrogen to about 190° C. and distill offmethanol with a good packed column. Keep column head temperature at 64°C., and gradually warm batch to 210° C. Cool after 160 g of methanol isremoved.

EXAMPLE 14 Polyester Amide External Oligomer Modifier

    ______________________________________                                        Ingredient           Grams                                                    ______________________________________                                        DBE-5                481                                                      dipropylene glycol   268                                                      Jeffamine D-230      115                                                      (polypropylene oxide diamine)                                                 butylstanoic acid    0.5                                                      ______________________________________                                    

Synthesized by same procedure as in Example 13.

EXAMPLE 15 Polyester External Oligomer Modifier

    ______________________________________                                        Ingredient       Grams                                                        ______________________________________                                        dipropylene glycol                                                                             4717                                                         adipic acid      4283                                                         triphenyl phosphine                                                                            1.2                                                          butylstanoic acid                                                                              3.0                                                          ______________________________________                                    

Synthesize as in Example 8, but do not use xylene. When column headtemperature drops to 80° C. acid number is about 20 mg KOH/g resin. Pulla vacuum of about 10 inches of Hg, and then gradually increase vacuum topull off remaining water. Final acid number is 3 mg KOH/g resin.

EXAMPLE 16

Latexes were prepared with the following generalized formula andsynthesized as described below.

    ______________________________________                                        a)   2122   g     deionized water                                                  8.5    g     MA-80 (dihexyl sulfosuccinate, Mona Chem.)                       5.4    g     ammonium acetate                                                 8.1    g     Na AMPS, 48% (Lubrizol Chemical)                                 10.5   g     A246L (Na olefin sulfonate, Rhone Poulenc)                  b)   7.4    g     Na formaldehyde sulfoxylate                                      10     ml    FeSO.sub.4 aqueous solution, 1000 ppm                       c)   869    g     vinyl acetate                                                    370    g     modifier as above from Examples 8 to 16                          3.1    g     acrylic acid                                                d)   6.3    g     ammonium persulfate                                              14     g     A246L                                                            159    g     deionized water                                             e)   874    g     vinyl acetate                                                    3.1    g     acrylic acid                                                f)   2.0    g     ammonium persulfate                                              27     g     deionized water                                             ______________________________________                                    

Weigh and mix thoroughly groups (a) and (c). Combine groups (a) and (c),stir with a spatula to disperse, and then emulsify for 5 minutes at10,000 rpm in a Ross ME 100L emulsifier. Add (b) ingredients to theemulsion, and warm in a 5 liter Morton flask to 50° C. with goodagitation under nitrogen. Pump in 40 ml of (d) over 2.5 hours, adjustingpumping rate to give a reaction temperature of about 55° C. Pump in therest of (d) and all of (e) over 3 hours. Pump in (f) over 1 hour. Cool.

EXAMPLES 17-24

Latexes approximately equivalent were prepared as in Example 16 andmixed with modifiers identified in Examples 8-15 as indicated in Table2.

                  TABLE 2                                                         ______________________________________                                        Ex.  Modifier DSC Tg   Knife Point MFFT                                                                          Dry Film Tack                              ______________________________________                                        17   Ex. 8     0       8.2         None                                       18   Ex. 9    11       8.8         None                                       19   Ex. 10   11       12.5        None                                       20   Ex. 11   10       13.7        None                                       21   Ex. 12   13       19.5        None                                       22   Ex. 13    6       7.6         None                                       23   Ex. 14   -5       10.0        Tacky                                      24   Ex. 15   --       16.5        None                                       ______________________________________                                         *DSC Tg's in degrees C. (single, distinct transitions are noted). MFFT =      minimum film formation temperature in degree C. (knife point). Tack and       MFFT were measured for dry latex films (only DSC Tg was measured for          modifiers).                                                              

The film from Example 23 is tacky at room temperature, while the otherlatexes form good, tack free films. The tack in Example 8 may be due toits very low Tg (-5° C.). Generally, Tg's in the 5°-10° C. range arepreferred. MFFT's of 20° C. or less are preferred, indicating that goodambient and low temperature film formation will occur. Example 23 wasmarginally tacky due to low Tg of the film.

EXAMPLE 25

A polyester oligomer modifier was prepared from the followingingredients synthesized by the procedure in Example 8. Mn=910andMw=1770.

    ______________________________________                                        Ingredient       Grams                                                        ______________________________________                                        adipic acid      2303                                                         diethylene glycol                                                                              2006                                                         butylstanoic acid                                                                              2.0                                                          ______________________________________                                    

EXAMPLE 26

A polyester modifier higher molecular weight was synthesized as inExample 1 to acid number 7, mg KOH/g resin. Mn=2570, Mw=5010.

    ______________________________________                                        Ingredient       Grams                                                        ______________________________________                                        adipic acid      330                                                          diethylene glycol                                                                              450                                                          butylstanoic acid                                                                              0.2                                                          ______________________________________                                    

EXAMPLE 27

A polyester modifier of high molecular weight was synthesized as inExample 1, add 4 g additional diethylene glycol (to correct for glycolloss) and advance to higher molecular weight. Mn=8810, Mw=29,600

    ______________________________________                                        Ingredient       Grams                                                        ______________________________________                                        diethylene glycol                                                                              326.6                                                        adipic acid      450                                                          butylstanoic acid                                                                              0.2                                                          ______________________________________                                    

EXAMPLES 28-32

Latex paints were made from the latex of Example 15 mixed with themodifiers in Examples 25-27.

    ______________________________________                                        Example  Modifier                                                             ______________________________________                                        28       Ex. 25                                                               29       Ex. 26                                                               30       Ex. 27                                                               31       DER 333N (190 epoxy eqv. wt., Dow Chemical)                          32       Poly THF 1000                                                                 (polytetramethylene oxide 1000 m. wt.)                               ______________________________________                                    

EXAMPLE 33

A latex was made from the following ingredients and synthesized asdescribed below.

    ______________________________________                                        a-1)     760    g      deionized water                                                 3.0    g      MA-80                                                           3.7    g      A246L                                                           1.9    g      ammonium acetate                                                3.1    g      Na AMPS                                                a-2)     312    g      vinyl acetate                                                   1.1    g      acrylic acid                                                    116    g      modifier (as above)                                    b)       2.6    g      Na formaldehyde sulfoxylate                            c)       3.7    ml     FeSO.sub.4 aqueous solution, 1000 ppm                  d)       0.61   g      ammonium persulfate                                             1.3    g      A246L                                                           31     g      deionized water                                        e)       1.7    g      ammonium persulfate                                             5.6    g      A246L                                                           42     g      deionized water                                        f)       330    g      vinyl acetate                                                   1.1    g      acrylic acid                                           g)       0.71   g      ammonium acetate                                                9.6    g      deionized water                                        ______________________________________                                    

Prepare mix a-1) and a-2), combine, and emulsify in an IKA works labemulsifier, model SD-50, at the finest setting for 5 minutes. Placeemulsion in a 2 liter Morton flask, and heat to 55° C. under nitrogen.Add (b) and (c), and then pump in (d) over 2.5 hours, controlling theexotherm at 55° C. Feed in mix (e) and (f) simultaneously over 2 hours,and then feed in (g) over 1 additional hour. Cool.

EXAMPLE 34

A vinyl acetate/butyl acrylate latex with polyester modifier wasprepared as in Example 33 above, but instead mix (a-2) below and mix (f)below were used as follows:

    ______________________________________                                        a-2)    280    g      vinyl acetate                                                   1.1    g      acrylic acid                                                    38.6   g      polyester modifier from Example 18                              70     g      butyl acrylate                                          f)      296    g      vinyl acetate                                                   74     g      butyl acrylate                                                  1.1    g      acrylic acid                                            ______________________________________                                    

EXAMPLE 35

A vinyl acetate/butyl acrylate latex with modifier was prepared as inExample 33 above but instead mix (a-2) and mix (f) below were used asfollows:

    ______________________________________                                        a-2)    265    g      vinyl acetate                                                   1.1    g      acrylic acid                                                    77.3   g      polyester modifier from Example 18                              66     g      butyl acrylate                                          f)      280    g      vinyl acetate                                                   70     g      butyl acrylate                                                  1.1    g      acrylic acid                                            ______________________________________                                    

The following is Table 3 listing properties for latex Examples 28-34.

                  TABLE 3                                                         ______________________________________                                        Example    Knife Point MFFT                                                                            Ambient Film Tack                                    ______________________________________                                        28         16° C. None                                                 29         19° C. None                                                 30         28° C. None                                                 31         >29° C.                                                                              None                                                 32         >29° C.                                                                              None                                                 33         17.4° C.                                                                             None                                                 34         16.3° C.                                                                             None                                                 ______________________________________                                    

The series of Examples 28, 29, and 30 illustrate the importance ofmodifier molecular weight. In moving from a polyester modifier with 2120Mn (Example 28) to a polyester modifier with 8810 Mn (Example 30), MFFTmoves from 16° C., which is normal for a latex with good low temperaturefilm formation properties, to 28° C., which is too high for acceptableambient and low temperature film formation. Increased amounts of thehigh molecular weight modifier will lower the MFT to an acceptablelevel. Examples 38 and 39 are unsatisfactory due to the composition andincompatibility of modifier.

EXAMPLE 36

A low molecular weight butyl carbitol diethylene glycol butylether/trimelitic anhydride triester modifier was prepared from thefollowing ingredients and synthesized as described below.

    ______________________________________                                        Ingredient           Grams                                                    ______________________________________                                        diethylene glycol butyl ether                                                                      1095                                                     trimelitic anhydride  435                                                     butylstanoic acid    0.5                                                      ______________________________________                                    

Stir under nitrogen in a 2 liter flask, and reflux off water with a goodpacked column, keeping head temperatures at 95° C. Cook at 190°-220° C.,cool after 6.5 hours.

EXAMPLES 37-42

Several latexes were made according to the recipe below containing thetriester modifier in Example 36 at triester levels indicated in eachexample 37-42 hereafter.

    ______________________________________                                        Example Number      Triester Level                                            ______________________________________                                        37                  0                                                         38                  25      g                                                 39                  75      g                                                 40                  100     g                                                 41                  125     g                                                 42                  150     g                                                 ______________________________________                                    

The above levels of triester were used in the following latex to form alatex paint containing the triester modifier.

    ______________________________________                                        a)   800    g     deionized water                                                  6.0    g     MM-80                                                            1.0    g     NaHC0                                                            1.0    g     NaAMPS.sup.3                                                b)   250    g     vinyl acetate                                                    2.0    g     WAM (wet adhesion ureidal? monomer, Alcolac                                   Chem.)                                                           (Z)    g     triester level as above                                     c)   2.0    g     ammonium persulfate                                         d)   250    g     vinyl acetate                                                    6.0    g     MT-70 (ditridecyl sulfosuccinate, Mona                                        Chemical)                                                   ______________________________________                                    

Blend mix (b) into mix (a) with a lab turbine at about 1000 rpm. Passthrough the flow through cell of an ultrasound unit at 85% (Sonics &Materials, VC-600). Heat to 67° C., hold 30 minutes, add (c) and hold1.5 hours. Pump in (d) over 3 hours, and cool.

                  TABLE 4                                                         ______________________________________                                        To determine the effect of modifier level on degree of                        plasticizer, a variety of VA homopolymer latexes were                         synthesized, as described in examples 45-50 which contain                     concentrations of triester ranging from 0 to 30% of the latex                 solids as noted in Examples 45-50. Glass transition                           temperature were determined by DSC, as described in the                       specification, with results of two DSC runs as follows:                       Ex.    Pct. Triester  Tg DSC(1) Tg DSC(2)                                     ______________________________________                                        45      0             38        36                                            46      5             13        30                                            47     15              6        13                                            48     20              0         6                                            49     25             -4         2                                            50     30             -12       -5                                            ______________________________________                                    

Run 1 involves cooling to -100° C., and scanning to 150° C. Run 2immediately follows run 1, and involves the same cooling and heatingprocesses. It is commonly accepted in the field of thermal analysis thatthe more reliable and practically-significant result is the one for run2.

This demonstrates the dependence of the Tg of the polymer-modifiermixture on the concentration of the plasticizing modifier. It alsodemonstrates the compatibility of the mixture, in that only singletransitions are observed.

EXAMPLES 43 and 44

Vinyl acetate homopolymer (Ex. 43) and vinyl acetate/butyl acrylatecopolymer (Ex. 44) were produced from the following ingredients.

    ______________________________________                                        Ex. 43    Ex. 44 (control)                                                    ______________________________________                                        a)   2022   g     2022 g   deionized water                                         7.2    g     7.2  g   MM-80                                                   4.3    g     4.3  g   ammonium acetate                                        5.4    g     --       SAM 181 surfactants (PPG Chemical)                      --           5.4  g   A246L                                              b)   35     g     28   g   vinyl acetate                                           --           7.0  g   butyl acrylate                                          0.7    g     0.7  g   ammonium persulfate                                c)   1700   g     1034 g   vinyl acetate                                           --           677  g   butyl acrylate                                          2.4    g     2.4  g   acrylic acid                                       d)   5.4    g     5.4  g   ammonium persulfate                                     21     g     21   g   A246L                                                   135    g     135  g   deionized water                                         12     g     --       SAM 181                                                 --           15   g   NaAMPS                                             e)   20     g     --       Triton X-100 (Rohm and Haas)                       ______________________________________                                    

Warm (a) to 71° C. under nitrogen with good stirring. Add (b) and allowexotherm to die (about 15 minutes). Pump in (c) and (d) in parallel over5 hours. Hold 1 hour and add (e) dropwise over 5 minutes. Mix 20 minutesand cool.

Example 45

Comparison of Soft Copolymer, Coalesced Hard Copolymer (Prior Art) WithCurrent Invention.

Prior art. Conventionally, the balance of low temperature film formationand absence of tack at ambient temperature is achieved by utilizing alatex composition with an elevated Tg, to achieve absence of tack, andthen temporarily reducing its Tg with a volatile coalescing solvent suchas Texanol, to achieve low temperature film formation. While this workswell, it also involves the emission of the coalescing solvent into theatmosphere, which contributes odor and air pollution. Example 44describes the synthesis of such a typical copolymer composition. Forthis experiment, that latex contained coalescing solvent at the level of6% to achieve a KMFT of 10° C. A film cast with this coalesced latex isnon-tacky at room temperature, but emits volatile solvent to theatmosphere.

Conversely, if one makes a copolymer with a low enough Tg to achieve lowtemperature film formation (60/40 VA/BA), it forms a film which isexcessively tacky at ambient use temperature. While this would involveno emissions to the atmosphere, it involves a commercially unacceptablebalance of properties. Example 28 describes the synthesis of a typicalsoft copolymer which achieves a KMFT of 10° C. on its own. A film castfrom this latex is extremely tacky at room temperature, but emits nosolvents to the atmosphere.

Present Invention. In the present invention, the use of a non-volatileexternal plasticizer accomplishes all three goals simultaneously: lowtemperature film formation, tack-free behavior at ambient temperatures,and no volatile organic emissions to the atmosphere. Example 43describes the synthesis of a vinyl acetate homopolymer containing 18%modifier, which achieves a KMFT (knife MFT) of 10° C. on its own. A filmcast from this latex is non-tacky at room temperature, and emits nosolvents to the atmosphere. The results are summarized as follows:

    ______________________________________                                                                           Organic                                    Approach      LTFF?   Ambient Tack (?)                                                                           Emissions?                                 ______________________________________                                        Coalesced hard latex                                                                        yes     no           yes                                        Soft copolymer                                                                              yes     yes          no                                         this invention                                                                              yes     no           no                                         ______________________________________                                    

EXAMPLE 46 Demonstration of Non-Volatile and Non-Migrating Behavior ofModifier.

A VA/BA 80/20 copolymer latex (example 44) was compared to a vinylacetate homopolymer latex coalesced conventionally with dibutylphthalate (DBP), one coalesced conventionally with Texanol, and to anexample of this invention (example 24) which was a VA homopolymercontaining a polyester external modifier. The Tg of films of the fourlatexes was monitored by DSC for up to 8 weeks, while the films wereaged at 140° F., to simulate accelerated aging of the films, and resultsare reported on Table 5.

                  TABLE 5                                                         ______________________________________                                        Latex     Initial Tg  Tg (8 wks)                                                                              Change in Tg                                  ______________________________________                                        hard copolymer                                                                          17          17         0                                            VA/DBP    12          31        19                                            VA/Texanol                                                                              10          32        22                                            Ex. 24     4           6         2                                            ______________________________________                                    

As expected, the untreated copolymer showed no change in Tg, since therewere no volatiles to be lost in the system. Also as expected, theconventionally coalesced latexes showed a substantial increase in Tg,due to the loss of the volatile coalescing solvent. However, example 24of this invention showed a negligible change, indicating that themodifier is essentially non-volatile.

An examination of the films showed that block resistance increased forthe coalesced samples over time, while it remained constant for theuntreated copolymer and for the example of this invention. Thisindicates that the modifier is also essentially non-migrating in nature.

EXAMPLE 47 Demonstration of Compatibility of Modifier in Matrix Polymer

The Tg's of the latex samples described in Table 4 were determined byboth DSC and DMA. In both cases, the samples exhibited single Tg's,which were intermediate between the Tg's of the components.Additionally, there was no evidence of Tg transitions characteristic ofeither of the individual components. This is strong evidence of thecompatibility the mixture of the modifier and the matrix polymer.

In addition, the Tg's of these same latex samples were compared to thosecalculated by the Fox relationship as described in the text. Thecomponent Tg's were -72° C. for the triester modifier, and 36° C. for VAhomopolymer parent polymer, as determined by DSC. Results are reportedin the following Table 6.

                  TABLE 6                                                         ______________________________________                                        Pct Modifier                                                                             Meas. Tg     Calc. Tg Difference                                   ______________________________________                                         0         36           --       --                                            5         30           28       2                                            15         13           13       0                                            20          6            6       0                                            25          2            0       2                                            30         -5           -7       2                                            ______________________________________                                    

This correlation between measured and calculated Tg's and the strongdependence of the Tg on the level of modifier, are strong evidence ofthe compatibility of the triester with the VA homopolymer.

We claim:
 1. An aqueous air-dry paint coating composition containing anemulsion polymerized polymeric binder free of organic coalescingsolvent, the polymeric binder comprising:a vinyl acetate polymercomprising polymerized vinyl acetate monomer containing an oligomerhaving a number average molecular weight between about 200 and 20,000and a Tg below about -20° C., the oligomer selected from a polyurethaneand a polyester, the polymeric binder containing between about 3% and50% by weight of said oligomer to provide a polymeric binder having a Tgless than 20° C., where said polymeric binder is produced by mixing theoligomer in the vinyl acetate monomer to provide an organic solution ofoligomer and vinyl acetate monomer, where said organic solution isdispersed into and polymerized in water to produce an oligomer modifiedvinyl acetate emulsion polymer where the oligomer is soluble in thepolymerized vinyl acetate monomer.
 2. The paint coating of claim 1 wherethe oligomer has a number average molecular weight between about 300 and10,000.
 3. The paint coating of claim 1 where the oligomer has a numberaverage molecular weight between about 500 and 5,000.
 4. The paintcoating of claim 1 where the oligomer has a Tg less than -40 ° C.
 5. Thepaint coating of claim 1 where the oligomer has a Tg less than -50° C.6. The paint coating of claim 1 where the organic solution is dispersedinto water to form an aqueous dispersion, and the aqueous dispersion ismicronized to a micronized aqueous dispersion having organic phaseparticle size droplets less than 5 microns prior to forming the oligomermodified vinyl acetate emulsion polymer.
 7. The paint coating of claim 6where the organic phase particle size droplets are less than 1 micron.8. The paint coating of claim 6 where the organic phase particle sizedroplets are less than 0.7 microns.
 9. The paint coating of claim 1where the vinyl acetate monomer is a monomer mixture of vinyl acetateand other ethylenically unsaturated monomer, and the monomer mixture isemulsion copolymerized to produce an oligomer modified vinyl acetateemulsion copolymer.
 10. The paint coating of claim 9 where thecopolymerized monomer mixture comprises between 80% and 100% by weightcopolymerized vinyl acetate monomer.
 11. The paint coating of claim 9where the copolymerized monomer mixture comprises at least 70% by weightcopolymerized vinyl acetate.
 12. The paint coating of claim 9 where thecopolymerized monomer mixture comprises between 40% and 100% by weightcopolymerized vinyl acetate.
 13. The paint coating of claim 1 where theoligomer is a polyurethane.
 14. The paint coating of claim 13 where thepolyurethane oligomer is a polyester-urethane copolymer.
 15. The paintcoating of claim 13 where the polyurethane oligomer is apolyether-urethane copolymer.
 16. The paint coating of claim 13 wherethe polyurethane oligomer is a polyurethane-urea copolymer.
 17. Thepaint coating of claim 1 where the polymeric binder contains between 105and 25% by weight of said oligomer.
 18. The paint coating in claim 1where the coating is free of volatile organic compounds.
 19. The paintcoating of claim 1 where the oligomer is a polyester polymer.
 20. Thepaint coating of claim 19 where the polyester oligomer is apolyester-amide copolymer.